Field emission apparatus is widely used in various equipment such as cathode ray tubes of displays, vacuum tubes for microwave technologies or sensors as electron sources.
A conventional field emission cathode apparatus comprises two important parts: a cathode electrode, and a grid electrode.
A cathode electrode comprises a metallic plane and cone shaped electron-emitters with upward apecies, which are made of a metal with a high melting point. Cone shaped electron-emitters are positioned on lattice points which are assumed on a metallic plane.
A grid electrode is a planar plate of a metal with a high melting point that is provided with circular holes, centers of which are positioned on lattice points assumed on a planar plate. Geometrical parameters of two sets of lattice points are the same.
Cathode and grid electrodes are combined so that, planar portions of these electrodes are parallel to each other, and an apex of each cone shaped electron-emitter is surrounded by an inner periphery of a circular hole of a grid electrode.
In this construction, when a voltage is applied between a cathode and a grid electrode, a high electric field is generated around an apex of an electron-emitter, and electrons are emitted from the apex, which is known as high field emission.
On a field emission cathode apparatus, however, several disadvantages have been pointed out.
(1) When there are random imperfections in shapes or dimensions of electron-emitters or a grid electrode, nonuniformity of electron emission arises over a whole emissive area of the apparatus. PA1 (2) When a breakdown arises between a electron-emitter and a grid electrode, there is no means to suppress a short circuit current, and a scale of damage is magnified. PA1 (3) There is no means to control magnitude of electron emission, and therefore this cathode apparatus is unsuitable for display means. PA1 metallic electron-emitters with pointed ends and a grid electrode which includes a metallic planar electrode provided with circular holes arranged on its surface, PA1 wherein each of the holes concentrically surrounds each of the electron-emitters, and a DC voltage for generating field emissions is applied therebetween, and PA1 active devices, each of which is connected to at least one electron-emitter in series, PA1 control an electric current supplied to at least one electron-emitter, and PA1 has a saturation characteristic of an electric current, and PA1 a withstand voltage higher than a voltage between the grid electrode and electron-emitters.